1. Field of the Invention
Embodiments of the present invention generally relate to obtaining hydrocarbon fluid from a wellbore. More specifically, embodiments of the present invention relate to connecting tubulars and drilling the wellbore using tubulars.
2. Description of the Related Art
To obtain hydrocarbon fluid from the earth, a wellbore is formed in the earth. The wellbore is typically drilled using a drill string having a drill bit connected to its lower end. The drill string is rotated and lowered into the earth to form the wellbore.
After the wellbore is drilled to a first depth, the drill string is removed from the wellbore. To prevent collapse of the wellbore wall, casing is often used to line the wellbore. Lining the wellbore involves lowering the casing into the drilled-out wellbore and setting the casing therein.
Casing is usually provided by the manufacturer in sections of a predetermined length; however, the length of casing which is desired for use in lining a section of the wellbore is often longer than the section length. To obtain the desired length of casing for use in lining the wellbore section, casing sections are often connected to one another to form a casing string. Typical casing sections are connected to one another by threaded connections.
Threadedly connecting casing sections to one another involves rotating one casing section relative to the other casing section. A first casing section is lowered partially into the wellbore and gripped by a gripping mechanism such as a spider to prevent rotational movement of the first casing section. The spider is located on or in the rig floor of a drilling rig disposed over the wellbore. A second casing section is then gripped and rotated relative to the first casing section to form the casing string by connecting the upper end of the first casing section to the lower end of the second casing section. Additional casing sections may be threadedly connected to the casing string in the same manner to add to the length of the casing string.
Various tools are utilized to rotate casing sections to make up these threaded connections (or break out the threaded connections when removing casing sections from the casing string) and to rotate the drill string to form the wellbore. One such tool is a top drive, which includes a motor for providing rotational force to the casing or drill string (both hereinafter referred to as “tubular”). The top drive is connected to the drilling rig and moveable relative thereto.
The lower end of the top drive is usually operatively connected to an apparatus for gripping the tubular so that the top drive is capable of rotating the tubular. The gripping apparatus is rotatable by the top drive relative to the top drive and the drilling rig.
Recently, an alternative method of lining the wellbore is proposed which involves drilling the wellbore with the casing which is used to line the wellbore, termed “drilling with casing.” In this method, the casing is rotated and lowered into the earth to form the wellbore. Casing sections may be threadedly connected to one another to form a casing string of a desired length or disconnected from one another to reduce the length of the casing string in a casing makeup or breakout operation. Drilling with casing is advantageous because drilling the wellbore and lining the wellbore is accomplished in only one step, saving valuable rig time and resources.
Some have suggested using the gripping apparatus in a drilling with casing operation to grip the casing and using the top drive to rotate the casing when drilling the casing into the wellbore and when making up or breaking out threaded connections. Using the gripping apparatus and the top drive in a drilling with casing operation is particularly attractive if the gripping apparatus and the top drive are capable of fluid flow therethrough to allow the typical circulation of fluid through the wellbore while drilling. The circulation of fluid through the casing and the wellbore removes the cuttings from the wellbore, the cuttings resulting from the drilling into the earth to form the wellbore.
Regardless of whether the operation involves drilling with casing or typical drilling and subsequent casing of the wellbore, existing top drives are only capable of imparting a specific range of torque to the drill string or casing. Often, because of their limited torque-providing capability, the existing top drives fail to supply sufficient torque to the drill string and/or casing to adequately affect the tubular drilling, running, and makeup and breakout operations. High output torque from the top drive is especially desirable for drilling with casing operations, as existing casing connections require torque above the capabilities of most currently-installed drives.
Therefore, it is desirable to provide additional torque capacity to a top drive system for use in rotating a tubular during running, drilling, and/or pipe handling operations. It is further desirable to provide this additional torque capacity for retrofitting to existing top drive systems.